revset: improve help on strings

mercurial/help/revsets.txt

@@ -5,10 +5,10 b' The language supports a number of predic'
 operators. Parenthesis can be used for grouping.
 
 Identifiers such as branch names must be quoted with single or double
-quotes if they contain characters outside of ``[a-zA-Z0-9]`` or if
-they match one of the predefined predicates. Special characters can be
-used in the identifiers by quoting them, e.g., ``\n`` is interpreted
-as a newline.
+quotes if they contain characters outside of
+``[._a-zA-Z0-9\x80-\xff]`` or if they match one of the predefined
+predicates. Special characters can be used in quoted identifiers by
+escaping them, e.g., ``\n`` is interpreted as a newline.
 
 There is a single prefix operator: